An aircraft is piloted by the actuation of piloting means, manually by a pilot, or automatically or semi-automatically via an automatic piloting device. Thus, an automatic piloting device may facilitate the control of the aircraft by the pilot, and provide better flight stability and safety, and may also servocontrol one or more flight parameters, such as the altitude, vertical speed, longitudinal speed, heading, etc., upon one or more setpoint values input by the pilot.
The actuation of the piloting means acts on members of the aircraft that are used to modify its flight dynamics, directly via a transmission chain or “rod linkage”, or by the action of a rod linkage on power members such as hydraulic valves, the latter case being the commonest, notably in large aircraft and the most sophisticated aircraft. For example, in a helicopter, a lateral or longitudinal movement of the control stick respectively acts on the lateral or longitudinal axis of the latter, that is to say on the pitch and roll control, by modifying the incidence of the blades of the main rotor. An action on the rudder bar controls the yaw of the helicopter, by modifying the incidence of the blades of the tail rotor. The incidence control of the blades of the various rotors is modified by mechanical actuators, for example electromechanical or hydromechanical actuators. Similarly, the incidence of elevators or rudders of an aeroplane, and the incidence of ailerons and flaps, can be modified by mechanical actuators. The latter may be linear actuators or rotary actuators.
There are also various types of mechanical actuators, notably actuators called “trim actuators” and actuators called “series actuators”. The “series actuators”, also designated “series screw jacks”, are placed in series with the flight controls, and comprise a body and an output spindle. The series actuators typically have a short response time and reduced authority. The latter are usually of the worm screw/nut type and are controlled by an electric motor. For example, for a linear series actuator, an electrical control causes a rotation of the spindle of the electric motor, and the rotation movement is converted into translation movement of the output spindle of the actuator relative to its body. The series actuators are said to be mechanically irreversible, which means that they are deformed only when an electrical control is applied to them. In particular, when the automatic piloting equipment is not operating, the series actuators have no effect on the control of the aircraft.
For safety reasons, it is standard practice to use redundancy of the actuators coupled to the automatic piloting equipment. Most of the aircraft equipment known from the state of the art has recourse to “slave” type actuators, that is to say actuators that have zero or limited intelligence. The latter in effect simply return position or speed information in a crude form, via sensors of potentiometer or resolver type, passive linear displacement sensors, commonly designated by the acronym LVDT, standing for “Linear Variable Differential Transformer”, or even passive rotation displacement sensors, commonly designated by the acronym RVDT, standing for “Rotary Variable Differential Transformer”. These actuators are normally powered or excited by external devices. Diagnosing their correct operation is generally reduced to sending a Boolean correct operation summary variable to a general monitoring module associated with the automatic pilot device.
In the interests of ongoing improvement to the safety of aircraft, whose piloting characteristics continually increase, a decentralization of the general monitoring intelligence has been observed, to the benefit of the actuator members themselves. Notably, self-monitoring and self-diagnosing of an actuator relative to the piloting controls that it receives should in particular enable it to react earlier (for example by self-disabling) and avoid placing the aircraft in a catastrophic piloting situation. Reaction time savings of a few tens to a few hundreds of milliseconds can thus be sought, in comparison to conventional centralized monitoring on a piloting chain.
Consequently, if a certain intelligence is transferred into the actuator, at the same time certain operating safety constraints concentrated in the automatic pilot system are transferred, notably the management of catastrophic failures. These safety constraints induced on the actuator that has become more independent lead to the implementation of particular architecture and monitoring principles, designed to satisfy the various safety constraints. Furthermore, it is desirable for these architectures, associated with a number of actuators in an aircraft, to be optimized in terms of integration and cost.